The invention relates to a wear adjusting device for disk brakes as well as to a method for controlling a wear adjusting device.
A wear adjusting device for pneumatically operated desk brakes is known, for example, from International Patent Document WO 91/19115. The disk brake according to International Patent Document WO 91/19115 having an application device on one side contains a cam lever which is rotatable about an axis parallel to the brake disk plane and preferably interacts by way of a traverse with one or two adjusting spindle(s) against which a brake lining is supported. The two adjusting spindles are coupled by a belt or a chain. A rotary drive, which can be driven by the cam lever, projects into a recess of the one adjusting spindle and, during the contact stroke causes a screwed connection of the adjusting spindle--and thus, by way of the toothed belt, also of the second adjusting spindle--in the approaching direction with the brake disk. The rotary drive contains a one-way rotary clutch as well as a torque-limiting or overload clutch by means of which an unintentional screwed connection of the adjusting spindles is avoided during the stall stroke and the release stroke.
Important elements of the above-mentioned brake adjustment are the one-way clutch and the overload clutch which are designed, for example, as systems operating in a frictionally engaged manner. For example, the one-way clutch operates as a wrap spring one-way clutch and the overload clutch operates as a friction slipping clutch or as an axial denture clutch. International Patent Document WO 91/19115 illustrates, for example, in FIG. 5 that the overload clutch is constructed in the roller bearing technology as a ball coupling whose shifting moment is caused exclusively by the geometry of the ramp-shaped pockets receiving the balls and by the extent of the prestressing force. This system has the advantages of being virtually free of frictional influences and permitting very high shifting moments in a small space. The one-way clutch of this embodiment is implemented as a grip roller clamping one-way clutch which has a very high response precision and permits the implementation of very high transmission moments in a small space.
The above-described adjusting device has had good results per se but requires several high-precision parts and therefore represents an object of the efforts of searching for further possibilities for lowering the manufacturing costs of pneumatic disk brakes.
Another adjusting device as well as a method for operating a vehicle brake is disclosed in German Patent Document DE 195 21 401 C1 corresponding to U.S. Pat. No. 5,568,845. It is a disadvantage in this case that, for overcoming the easing play by the adjusting device, the operating time or reaction time of the brake is increased. The present invention relates to the described problems and provides an adjusting device which, in industrial-scale manufacturing, permits a clear reduction of cost in comparison to the above-described system. The characteristics of the solution are preferably a--particularly electronically commutated--direct-current geared motor or possibly a stepping motor is arranged in the brake-integrated control unit such that the transmission output element acts in the sense of a rotary operation onto the wear adjusting mechanism of the brake.
Although disk brakes operated by electric motors have been known for a long time, because of the numerous problems with respect to their implementation (cost, resistance to failure, etc.), they have not been success in practice. The invention uses a different approach in that it remains with the concept of a pneumatically applied disk brake and only the adjusting of the brake is carried out by an electric drive. Thus, the invention ideally combines the advantages of a pneumatically operated disk brake (safety, reliability) with the advantages of an electric drive (low cost). In addition, by means of an electric drive, the response time is reduced during the adjusting of the brake; the required easing play can be reduced to a very low value as a result of the adjustment between brake operations according to the invetion; and the air consumption (for example, the emergy consumption connected with generating the air) of the pneumatic system is reduced.
In the case of two-spindle brakes, the intervention preferably takes place upon the synchronization mechanism (such as a chain). In the case of single-spindle brakes, it takes place preferably directly upon the wear adjusting element (adjusting spindle).
Advantageous further developments of the invention are contained in the subclaims.
The invention also solves the problem of operating an electric-motor-driven adjusting device for a pneumatically operated brake in a manner which is as simple and reliable as possible. The characteristics for solving this problem are the following sequence of steps:
Step A: Immediately after complete reduction of the operating pressure in the brake cylinder preferably a pneum another adjusting movement of the adjusting spindles is carried out which is dimensioned such that a complete elimination of the easing play is achieved.
Step B: Then the adjusting mechanism (the adjusting spindles) are set back by the electric drive by a defined amount which corresponds to a given desired easing play.
This type of adjustment has the following advantages: Since, when the brake is operated, the easing play is conventionally overcome by the rotary lever, the eccentric traverse and the piston, the response time of the brake is shortened. The required brake cylinder stroke and thus also the consumption of pressure energy is reduced because of the low required easing play which is adjusted exclusively between two brake operations. Since, after each operation of the brake, the easing play is newly adjusted in a precise manner, a very uniform easing play is, in addition, obtained under all operating conditions. In the event of a servicing, considerable time is saved because of the fact that all brakes of the vehicle can automatically be moved into the servicing position for the exchange of the brake lining and the easing play adjustment after the termination of the servicing also takes place automatically.
After each operation of the brake, the wear adjusting mechanism is triggered in the sense of an application until the easing play approaches zero. Subsequently, the adjusting mechanism is set back by way of the motor operator by a given amount which corresponds to the desired easing play. Thus, after the reduction of the operating pressure of the brake cylinder, an operating pulse is given in the sense of an application which is so long that a complete elimination of the easing play is achieved. Immediately following this application pulse, the setting back will then take place to the required desired easing play.
As an alternative for reducing the operating frequency of the adjusting mechanism, the above-described sequence may in each case only take place after a given number of brake operations.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.